Diamonds and other gemstones are often analyzed and graded by multiple trained and skilled individuals, based upon their visual appearance. For example, the foundation of diamond analysis comprises analysis of the Four C's (color, clarity, cut and carat weight), two of which, color and clarity, have been traditionally evaluated by human inspection. Gemstones are also assessed for unusual visual qualities. For example, certain gemstones produce fluorescence emission under UV illumination, the extent and distribution of such fluorescence are also used to grade such gemstones. Like color and clarity grading, fluorescence grading was previously primarily assessed based on human visual perception. Analysis and grading requires the exercise of judgment, the formation of opinions and the ability to draw fine distinctions based on visual comparisons.
A process of inspection and analysis is often time-consuming, involving multiple rounds of inspections, measurements and checks by each trained and experienced individual. The process also involves quality control and may include a variety of non-destructive tests to identify treatments, fillings or other defects that may affect the quality of a specimen. Finally, the process includes intensive visual comparison of the diamond with a reference set of diamond master stones that serve as a historical standard with respect to diamond color and fluorescence.
Instruments have been created to improve efficiency and to permit gemstone analysis in the absence of trained and experienced individuals. For example, U.S. Pat. No. 7,102,742 to Geurtz et al. discloses a gemstone fluorescence measuring device that includes an ultraviolet (“UV”) emission chamber, a UV radiation source, and a light meter assembly. The UV radiation source includes an upper light emitting diode (“LED”) and a lower LED that radiate a gemstone under test from both above and below the gemstone. However, current instrument cannot provide consistent and reproducible fluorescence grade to fancy shape cut stones; such gemstones that are classified as Step Cuts, Hearts, Marquises, Ovals, Pears, Triangles, Princess cut, or any other cuts rather than round brilliant cut (RBC). Additionally, current instrument cannot provide hue information and an operator must input the color of fluorescence manually. This leads to the incorrect grading since it is not easy to see the color of weak fluorescence by human eyes.
What is need are apparatus and methods that can provide gemstone assessment and grading (e.g., fluorescence grading) as consistent and accurate as assessment and grading provided by trained and experienced individuals.